# FBD for car slowing down?

1. Jun 5, 2016

### alaa amed

1. The problem statement, all variables and given/known data

A car is coasting to the right and slowing down. Neglect air resistance
Draw free body diagram.
2. Relevant equations
N/A

3. The attempt at a solution

I drew the normal and the force of gravity equal and opposite of each other in the vertical direction. However, I am little confused about the direction of the force of friction. I know that the velocity vector should be pointing to the right and the acceleration vector should be pointing to the left since the car is slowing down, but what does that mean for the force of friction?

Thanks,

2. Jun 5, 2016

### nrqed

Hint: $\vec{F_{net}} = m \vec{a}$

3. Jun 6, 2016

### CWatters

Perhaps consider a wheel subject to braking. Which way is the wheel trying to slide relative to the road. What does that tell you about the direction of the friction force?

4. Jun 6, 2016

### haruspex

While that works, I recommend nrqed's hint since that does not depend on the ultimate cause of the slowing. It encompasses axle friction and rolling resistance.
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